1. Field of the Invention
The present invention relates to the connecting of high capacity electric terminals. More particularly, the present invention relates to the structure that connects a power supply unit of semiconductor device manufacturing equipment to a power source.
2. Description of the Related Art
In general, various units of semiconductor device manufacturing equipment, such as photolithography equipment, ion-implanting equipment, thin film deposition equipment, and etching equipment, are used to perform respective unit processes in the manufacturing of a semiconductor device. Most of such equipment consumes a large amount of electric energy. Therefore, such semiconductor equipment is connected with high capacity power cables through which a large amount of electric power is supplied to the equipment.
More specifically, a power supply unit supplies and distributes electric power to the various different units of the conventional semiconductor device manufacturing equipment. The power supply unit includes a circuit breaker for automatically interrupting the power supply in an emergency or when the manufacturing equipment begins to consume an unduly large amount of energy in excess of some predetermined amount. The power supply unit also includes a main high capacity electrical terminal. The terminal is connected by a nut and bolt to a high capacity electrical terminal of a power cable of a main power source. Electrical power for each unit of semiconductor device manufacturing equipment is thus supplied from the main power source through the high capacity electric terminals.
Most of the high capacity power cables are thick and heavy so that large amounts of electric power can be supplied therethrough. Therefore, a worker must secure the nut and bolt tightly to connect the terminal of the power supply unit with that of the power source to prevent the terminals from disconnecting under the weight of the power cable, or from swinging relative to one another due to external forces.
Also, the point at which the terminals are connected is small. The force of the joint is thus concentrated at this point. Therefore, the terminal is often bent or broken when the nut and the bolt are tightened securely enough to connect the terminal of the power supply unit with the high capacity terminal of the power cable leading to the main power source.
Moreover, compressive stress is inversely proportional to the area over which it is applied. Therefore, the stress at the small area of the point of connection of the two terminals becomes increasingly high as the nut and the bolt are tightened. This small area and its surroundings where the compressive stress is great can be heated rather easily by the current flowing through the contact area. Heat generated in this way eventually poses a fire risk.
Still further, the threads of the nut and bolt can be stripped when the nut and the bolt are tightened with excessive force. On the contrary, if the force exerted to tighten the nut and the bolt is too small, the two terminals joined by the nut and the bolt are free to swing or slide relative to each other. The friction created by such relative movement heats up the point of connection between the two terminals.